After the making of a web of paper in a paper machine, dust and impurities adhere to the face of the paper web, such as debris and fibers derived from the dryer section of the paper machine. A further important source of dust is, for example, the creping process. The dust that is separated from the face of the paper web, especially when the web is unwound, for example, in a slitter-winder, spreads in the paper mill and in the finishing into the environment, i.e., into the machine hall in which the paper machine is situated. This dust that spreads into the environment causes several problems and associated drawbacks. The most important drawback is the contamination of breathing air in the working environment beyond permitted limits. Another important drawback being the substantially increased risk of fire due to the presence of the dust.
In the machine hall, as a rule, an air flow is present that flows from the dry end of the hall, where, for example, the slitter-winder is placed, towards the wet end of the hall. A part of the dust that floats in the air, and in fact a major part, rests as a deposit on various equipment surfaces present in the hall, such as on the frame beams of the machine, on crane rails, and on various ducts and pipes, whose daily cleaning is quite difficult. Some of these equipment surfaces, such as a part of the Yankee hood and its related devices, are also very hot and may ignite the dust settling thereon.
From the prior art, devices are known by whose means attempts are made to remove dust from the web locally, for example, by means of dust-removing boxes. Such boxes are placed in suitable locations, for example, in the vicinity of the slitter-winder. With respect to the prior art related to this type of devices, reference is made, e.g., to U.S. Pat. Nos. 4,715,078 and 3,239,863.
In U.S. Pat. No. 4,715,078, a method and a device are described for cleaning the edges of a paper web at a slitter-winder and for removing the dust detached from the edges. In the device shown in this reference, two cleaning rolls are used, which are placed strategically in the path of running of the paper web. The first cleaning roll contacts the forward edge of the paper web when the paper web runs further from the slitter. At the same time as the paper web runs further, its upper face is also cleaned by the same roll. The second cleaning roll cleans the rear edge of the paper web as it runs further. By means of the second cleaning roll, the lower face of the paper web is also cleaned. After this, by means of a vacuum system, the particles and dust that are detached by the cleaning rolls are removed, and all of the four edges of the paper web are also cleaned. The pressure system removes the particles from the face of the paper web so that they can be carried off by means of the vacuum system.
In U.S. Pat. No. 3,239,863, a web cleaning device is described, in which a chamber space is employed, in which two air nozzles directed towards the web have been formed. The space between the nozzles is closed so that it forms an exhaust chamber for the air discharged from the nozzles and for the dust detached from the web.
It is one particular problem of these prior art devices that they are local, i.e., their fields of application are quite dependent on the lay-out of the paper finishing device that is used, such as the slitter-winder. In a number of applications in which a paper web is unwound, there are several sources of dust from which dust is liberated into the hall. Thus, from two even up to five devices based on local dust removal are needed for each unwind station, in which case the dust-removing system becomes quite spacious and complicated.